In recent years, with the spread of computers, ink jet printers have been widely used to print on paper, film, cloth, etc. at offices as well as at home.
Examples of ink jet recording method include a method which allows a piezoelectric element to give pressure that causes a droplet to be ejected, a method which comprises heating the ink to generate bubbles, causing a droplet to be ejected, a method involving the use of ultrasonic wave, and a method which uses electrostatic force to suck and discharge a droplet. As inks for these ink jet recording methods there are used aqueous inks, oil-based inks and solid (melt type) inks. Among these inks, aqueous inks are mainly used from the standpoint of producibility, handleability, odor, safety, etc.
The dyes to be incorporated in these inks for ink jet recording are required to exhibit a high solubility in solvents, allow a high density recording and have a good hue and an excellent fastness to light, heat, air, water and chemical, a good fixability to image-receiving materials, difficulty in running, an excellent preservability, no toxicity and a high purity and be available at a low cost.
However, it is extremely difficult to seek dyes meeting these requirements to a high extent. In particular, dyes having a good cyan hue and an excellent weathering resistance have been keenly desired.
Various dyes and pigments have been already proposed for ink jet recording and have been actually used. However, no dyes meeting all these requirements have been found yet. Known dyes and pigments provided with color index (C.I.) can difficultly satisfy both the hue and fastness requirements for inks for ink jet recording. As dyes which enhance fastness there have been proposed azo dyes derived from aromatic amines and 5-membered heterocyclic amines in JP-A-55-161856. However, these dyes are disadvantageous in that they assume an undesirable hue in the yellow and cyan ranges and thus cause deterioration of color reproducibility. Inks for ink jet recording which are intended to satisfy requirements for both hue and light-fastness are disclosed in JP-A-61-36362 and JP-A-2-212566. However, the dyes used in these patents, if used as water-soluble inks, leave something to be desired in solubility in water. Further, when the dyes described in these patents are used as water-soluble inks for ink jet, problems arise with moist heat fastness as well. As a means for solving these problems there has been proposed the use of the compound and ink described in JP-T-11-504958 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application). Further, reference has been made to inks for ink jet recording comprising pyrazolylaniline azo for improving hue or light-fastness (Japanese Patent Application No. 2000-80733). However, these inks for ink jet recording leave something to be desired in both color reproducibility and fastness of outputted image.
It has been further made obvious that images recorded on an ink jet photographic grade gloss paper sometimes show a remarkably poor preservability when posted indoor. The inventors presume that this phenomenon is attributed to some oxidizing gas in the air such as ozone. This phenomenon no longer occurs when the flow of air is blocked by some measure such as putting in glass-fronted frame.
This phenomenon occurs remarkably with ink jet photographic grade gloss paper and thus brings forth a great problem with the related art ink jet recording process featuring photographic grade as one of its important advantages.
Therefore, an aim of the present invention is to provide an ink for ink jet recording comprising an aqueous ink which allows ejection with a high stability and gives an image having a good hue, an excellent light-fastness and water resistance, no defects in image quality such as running of fine line and a good preservability under severe conditions from the standpoint of handleability, odor, safety, etc. Another aim of the present invention is to provide an ink set which allows ejection of even an ink aged over an extended period of time or under severe conditions with a high stability.
Disclosure of the Present Invention
The characteristic of the ink for ink jet recording of this invention is that an ink for ink jet recording having the following phthalocyanine dye dissolved or dispersed in an aqueous medium has at least one of the following properties. Preferred is an ink that satisfies all the following requirements (1) to (4).    (1) The viscosity of the aforementioned ink at 25° C. is from 1 to 50 mPa·sec, preferably from 1 to 20 mPa·sec.    (2) The conductivity of the aforementioned ink is from not smaller than 0.01 S/m to not greater than 10 S/m.    (3) The static surface tension of the aforementioned ink at 25° C. is from 25 to 50 mN/m.    (4) The percent change of viscosity and surface tension of the aforementioned ink from at 25° C. to at 10° C. is not greater than 250% and not greater than 130%, respectively.
The characteristic of the process for the production of an ink for ink jet recording of this invention is that the process for the production of an ink for ink jet recording comprises at least a step of applying ultrasonic vibration and/or in the process for the production of an ink for ink jet recording, the ink for ink jet recording thus prepared is filtered through a filter having pores of an effective diameter of not greater than 1 μm and defoamed before use.
The aforementioned aims of this invention were solved by the following desirable means.
1. An ink for ink jet recording, comprising a aqueous medium and a phthalocyanine dye dissolved or dispersed in the aqueous medium, wherein the phthalocyanine dye is a water-soluble dye having an oxidation potential of more positive than 1.0 and the ink has a conductivity of 0.01 S/m to 10 S/m.
2. The ink for ink jet recording according to the preceding Paragraph 1, which has a viscosity of 1 to 20 mPa·sec at 25° C.
3. The ink for ink jet recording according to the preceding Paragraph 1 or 2, which has a static surface tension of 25 to 50 mN/rn at 25° C.
4. The ink for ink jet recording according to the preceding Paragraph 2 or 3, wherein a viscosity of the ink has a viscosity ratio of not greater than 250% from at 25° C. to at 10° C., and a static surface tension has a static surface tension ratio of not greater than 130% from at 25° C. to at 10° C.
5. The ink for ink jet recording according to any one of the preceding Paragraphs 1 to 4, which has a pH value of 4 to 12 at 25° C.
6. The ink for ink jet recording according to any one of the preceding Paragraphs 1 to 5, which has a dye remaining ratio(density afler fading/initial density×100) of not smaller than 60% (preferably 80%) afler 24 hours of storage in an atmosphere of 5 ppm ozone in a monochromatic area that is obtained by printing with a monochromatic ink(cyan) in such a manner a cyan reflection density through a status A filer is from 0.9 to 1.1.
7. The ink for ink jet recording according to any one of the preceding Paragraphs 1 to 6, wherein the ink has Cu ions that are eluted with water in an amount of not greater than 20% of a total amount of the dye afler an ozone fading under the conditions defined in 6.
8. The ink for ink jet recording according to any one of the preceding Paragraphs 1 to 7, wherein the phthalocyanine dye is the water-soluble dye having an electron-withdrawing group at β-position of a benzene ring in the phthalocyanine.
9. The ink for ink jet recording according to any one of the preceding Paragraphs 1 to 8, wherein the phthalocyanine dye is the water-soluble dye that is produced by a process which doesn't pass through a sulfonati ozone fading on of an unsubstituted phthalocyanine.
10. The ink for ink jet recording according to any one of the preceding Paragraphs 1 to 9, wherein the phthalocyanine dye is represented by the following formula (I):
wherein X1, X2, X3 and X4 each independently represent —SO-Z, —SO2-Z, —SO2NR1R2, sulfo group, —CONR1R2 or —CO2R1; Z represents a substituted or unsubstituted alkyl group, substituted or unsubstituted cycloalkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted aralkyl group, substituted or unsubstituted aryl group or substituted or unsubstituted heterocyclic group; R1 and R2 each independently represent a hydrogen atom, substituted or unsubstituted alkyl group, substituted or unsubstituted cycloalkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted aralkyl group, substituted or unsubstituted aryl group or substituted or unsubstituted heterocyclic group; and when there are a plurality of Z's, they may be the same or different;Y1, Y2, Y3 and Y4 each independently represent a monovalent substituent; and when there are a plurality of any of X1 to X4 and Y1 to Y4, they may be the same or different;a1 to a4 and b1 to b4 represent the number of substituents X1 to X4 and Y1 to Y4, respectively; a1 to a4 each independently represent an integer of from 0 to 4 and are not 0 at the same time; and b1 to b4 each independently represent an integer of 0 to 4; andM represents a hydrogen atom, metal atom or oxide, hydroxide or halide thereof.
11. The ink for ink jet recording according to the preceding Paragraph 10, wherein the dye represented by the formula (I) is a dye represented by the following formula (II):
wherein X11 to X14, Y11 to Y18 and M1 each have the same meaning as those in the formula (I); and a11 to a14 each independently represent an integer of 1 to 2.
12. A method for ink jet recording, comprising using the ink for ink jet recording according to the preceding Paragraphs 1 to 11.
13. A method for recording an image on an image-receiving material, comprising ejecting an ink droplet onto the image-receiving material including an image-receiving layer containing an inorganic white particulate pigment on a support according to a record signal,
wherein the ink droplet comprises the ink for ink jet recording described in the preceding Paragraphs 1 to 11.
14. A method for producing the ink for ink jet recording according to the preceding Paragraphs 1 to 11, which comprises at least applying a ultrasonic vibration.
15. A method for producing the ink for ink jet recording according to the preceding Paragraphs 1 to 11,
wherein the ink for ink jet recording prepared is filtered through a filter having pores of an effective diameter of not greater than 1 μtm and defoamed before use.